The present invention relates generally to internal combustion fuel injection systems. More particularly, the present invention relates to unit injectors employed in fuel injection systems.
In fuel injection systems to which the present invention relates, a pump plunger pressurizes fuel within an injector. When the fuel reaches a sufficient pressure, a valve is lifted from a valve seat and pressurized fuel is injected through a discharge orifice of the injector nozzle. The pump plunger directly or indirectly follows a cam profile of an injection train to pressurize fuel within the injector. The fuel is injected into the engine cylinder for a period of time prior to combustion. The latter time period is often referred to as the ignition delay period. At the expiration of the ignition delay period, a portion of the injected fuel which has fully mixed with intake air combusts in a relatively spontaneous manner. This uncontrolled combustion results in high combustion noise and the generation of a relatively high quantity of oxides of nitrogen emissions. Because of increasing governmental and regulatory demands to control emissions and increase fuel economy, newer engine design parameters tend to require higher injection pressures and shorter durations for the injected charges. The implementation of limitations on the quantity of fuel which is injected during the ignition delay period is desirable for high pressure/short duration fuel charges.
U.S. patent application Ser. No. 854,047 filed Apr. 21, 1986 entitled "Method and Apparatus for Regulating Fuel Injection Timing and Quantity" and assigned to the assignee of the present invention discloses a fuel injection system which employs a solenoid valve for precisely regulating the fuel injection timing. The intake charge quantity of fuel supplied through a charge pump is precisely regulated during each intake stroke and the quantity of injected fuel is precisely regulated by a spill termination of the high pressure delivery. During each stroke an electronic controller having a data processor energizes and deenergizes the solenoid valve for adjusting the fuel injection timing and the quantity of fuel in the injected charge.
U.S. Pat. No. Re. 30,189 of Julius P. Perr entitled "Fuel Injection System For Diesel Engines" discloses an injection rate control device employing an auxiliary spring which is connected in line with the conventional injection train to operate an injector plunger in synchronism with the rotation of a cam shaft. The auxiliary spring has a lower spring rate than that of the injection train so that the injector plunger advances at a different rate when it is under the control of the auxiliary spring. Means are included for rendering the auxiliary spring ineffectual during a portion of the plunger advancement. The rate of plunger advance is controlled by the auxiliary spring during the initial portion of the advancing stroke and by the conventional injection train during the balance of the advancing stroke. The auxiliary spring automatically varies the ignition timing and the injection rate. Fuel may be injected into the cylinder at a relatively slow rate during an initial phase of the ignition delay interval and at a fast rate during the balance of the injection stroke of the injector plunger.